The broad objective of this project is to elucidate the separate and combined effects of microbial and photolytic processes on transformations of target Superfund chemicals, with applications to gaining a better understanding of natural transformation processes at existing Superfund sites and to developing improved systems for remediation. These chemicals will include organophosphate pesticides (chlorpyrifos, parathion, and diazonon) and polycyclic aromatic hydrocarbons (fluorene and its heterocyclic analogs carbazole, dibenzofuran, and dibenzothiophene; fluoranthene; and benzo[a]pyrene). This work will yield important information regarding the fundamental processes affecting toxic exposures in natural systems, and it will include the development of new strategies for decreasing these exposures through improved remediation systems. The specific aims of this project are as follows. (1) Assess the separate photolytic and microbial isolate transformations of individual target Superfund chemicals. (2) Determine photolytic and microbial transformation effects on toxicity and identify intermediates of interest. (3) Assess biodegradability of photolytic intermediates and photodegradability of biodegradation intermediates. (4) Evaluate influence of physical, chemical, and biological factors on microbial and photolytic degradation, including mixture effects. (5) Develop and evaluate novel remediation technologies based on an innovative combination of photolytic, oxidative, and microbial transformation processes. This work will interface strongly with the other Projects in this proposal through its focus on the same OPs and PAHs, and through it's use of their toxicity assays to assess the toxicity of photolytic and microbial intermediates.